Elevated oxidative membrane damage associated with genetic modifiers of Lyst-mutant phenotypes

Minimal phenotypes in transgenic mice with the human LOXL1/LOXL1-AS1 locus associated with exfoliation glaucoma

Exfoliation syndrome is a leading cause of secondary glaucoma worldwide. Among the risk-factors for exfoliation syndrome and exfoliation glaucoma that have been investigated, a genetic association with 15q24.1 is among the most striking. The leading candidates for the causal gene at this locus are LOXL1 and/or LOXL1-AS1, but studies have not yet coalesced in establishing, or ruling out, either candidate. Here, we contribute to studies of the 15q24.1 locus by making a partially humanized mouse model in which 166 kb of human genomic DNA from the 15q24.1 locus was introduced into the mouse genome via BAC transgenesis (B6-Tg(RP11-71M11)Andm). Transgenic expression of human genes in the BAC was only detectable for LOXL1-AS1. One cohort of 34 mice (21 experimental hemizygotes and 13 non-carrier control littermates) was assessed by slit-lamp exams and SD-OCT imaging at early (1-2 months) and mid (4-5 months) time points; fundus exams were performed at 5 months of age. A second smaller cohort (3 hemizygotes) were aged extensively (>12 months) to screen for overt abnormalities. Across all genotypes and ages, 136 slit-lamp exams, 128 SD-OCT exams, and 42 fundus exams detected no overt indices of exfoliation syndrome. Quantitatively, small, but statistically significant, age-related declines in ganglion cell complex thickness and total retinal thickness were detected in the hemizygotes at 4 months of age. Overall, this study demonstrates complexity in gene regulation from the 15q24.1 locus and suggests that LOXL1-AS1 is unlikely to be a monogenic cause of exfoliation syndrome but may contribute to glaucomatous retinal damage.

Lack of evidence for GWAS signals of exfoliation glaucoma working via monogenic loss-of-function mutation in the nearest gene

PURPOSE

Exfoliation syndrome (XFS) is a systemic disease of elastin-rich tissues involving a deposition of fibrillar exfoliative material (XFM) in the anterior chamber of the eye, which can promote glaucoma. The purpose of this study was to create mice with CRISPR/Cas9-induced variations in candidate genes identified from human genome-wide association studies (GWAS) and screen them for indices of XFS.

METHODS

Variants predicted to be deleterious were sought in the Agpat1, Cacna1a, Loxl1, Pomp, Rbms3, Sema6a, and Tlcd5 genes of C57BL/6J mice using CRISPR/Cas9-based gene editing. Strains were phenotyped by slit-lamp, SD-OCT imaging, and fundus exams at 1-5 mos of age. Smaller cohorts of 12-mos-old mice were also studied.

RESULTS

Deleterious variants were identified in six targets; Pomp was recalcitrant to targeting. Multiple alleles of some targets were isolated, yielding 12 strains. Across all genotypes and ages, 277 mice were assessed by 902 slit-lamp exams, 928 SD-OCT exams, and 358 fundus exams. Homozygosity for Agpat1 or Cacna1a mutations led to early lethality; homozygosity for Loxl1 mutations led to pelvic organ prolapse, preventing aging. Loxl1 homozygotes exhibited a conjunctival phenotype of potential relevance to XFS. Multiple other genotype-specific phenotypes were variously identified. XFM was not observed in any mice.

CONCLUSIONS

This study did not detect XFM in any of the strains. This may have been due to species-specific differences, background dependence, or insufficient aging. Alternatively, it is possible that the current candidates, selected based on proximity to GWAS signals, are not effectors acting via monogenic loss-of-function mechanisms.

TYRP1 Protects Against the Apoptosis and Oxidative Stress of Retinal Ganglion Cells by Binding to PMEL

OBJECTIVES

This research aimed to dissect the function of TYRP1 and PMEL in glaucomatous animal and cell models.

METHODS

A chronic ocular hypertension (COH) rat model was induced in the right eyes of rats through the electrocoagulation of superficial iris veins. In addition, an oxygen-glucose deprivation (OGD)-retinal ganglion cell (RGC) model was constructed through OGD. TYRP1 and PMEL expression was altered in the animal and cell models to explore their effects.

RESULTS

TYRP1 and PMEL expression was poor in glaucoma patients, COH rats, and OGD-RGCs. Mechanistically, TYRP1 interacted with PMEL to upregulate PMEL in OGD-RGCs. TYRP1 overexpression enhanced viability and diminished apoptosis and oxidative stress of OGD-RGCs, which was abolished by PMEL knockdown. TYRP1 upregulation reduced intraocular pressure, RGC apoptosis, and oxidative stress in COH rats, which was reversed by PMEL knockdown.

CONCLUSIONS

TYRP1 elevates PMEL expression to reduce RGC apoptosis and oxidative stress in vivo and in vitro.

LYST deficiency impairs autophagic lysosome reformation in neurons and alters lysosome number and size

Chediak-Higashi syndrome (CHS) is a rare, autosomal recessive disorder caused by biallelic mutations in the lysosomal trafficking regulator (LYST) gene. Even though enlarged lysosomes and/or lysosome-related organelles (LROs) are the typical cellular hallmarks of CHS, they have not been investigated in human neuronal models. Moreover, how and why the loss of LYST function causes a lysosome phenotype in cells has not been elucidated. We report that the LYST-deficient human neuronal model exhibits lysosome depletion accompanied by hyperelongated tubules extruding from enlarged autolysosomes. These results have also been recapitulated in neurons differentiated from CHS patients' induced pluripotent stem cells (iPSCs), validating our model system. We propose that LYST ensures the correct fission/scission of the autolysosome tubules during autophagic lysosome reformation (ALR), a crucial process to restore the number of free lysosomes after autophagy. We further demonstrate that LYST is recruited to the lysosome membrane, likely to facilitate the fission of autolysosome tubules. Together, our results highlight the key role of LYST in maintaining lysosomal homeostasis following autophagy and suggest that ALR dysregulation is likely associated with the neurodegenerative CHS phenotype.

Chediak-Higashi syndrome: a review of the past, present, and future

Since the initial description of Chediak-Higashi syndrome (CHS), over 75 years ago, several studies have been conducted to underscore the role of the lysosomal trafficking regulator (LYST) gene in the pathogenesis of disease. CHS is a rare autosomal recessive disorder, which is caused by biallelic mutations in the highly conserved LYST gene. The disease is characterized by partial oculocutaneous albinism, prolonged bleeding, immune and neurologic dysfunction, and risk for the development of hemophagocytic lympohistiocytosis (HLH). The presence of giant secretory granules in leukocytes is the classical diagnostic feature, which distinguishes CHS from closely related Griscelli and Hermansky-Pudlak syndromes. While the exact mechanism of the formation of the giant granules in CHS patients is not understood, dysregulation of LYST function in regulating lysosomal biogenesis has been proposed to play a role. In this review, we discuss the clinical characteristics of the disease and highlight the functional consequences of enlarged lysosomes and lysosome-related organelles (LROs) in CHS.

Mouse models and strain-dependency of Chédiak-Higashi syndrome-associated neurologic dysfunction

Chédiak-Higashi syndrome (CHS) is a lethal disorder caused by mutations in the LYST gene that involves progressive neurologic dysfunction. Lyst-mutant mice exhibit neurologic phenotypes that are sensitive to genetic background. On the DBA/2J-, but not on the C57BL/6J-background, Lyst-mutant mice exhibit overt tremor phenotypes associated with loss of cerebellar Purkinje cells. Here, we tested whether assays for ataxia could measure this observed strain-dependency, and if so, establish parameters for empowering phenotype- and candidate-driven approaches to identify genetic modifier(s). A composite phenotypic scoring system distinguished phenotypes in Lyst-mutants and uncovered a previously unrecognized background difference between wild-type C57BL/6J and DBA/2J mice. Accelerating rotarod performance also distinguished phenotypes in Lyst-mutants, but at more advanced ages. These results establish that genetic background, Lyst genotype, and age significantly influence the severity of CHS-associated neurologic deficits. Purkinje cell quantifications likewise distinguished phenotypes of Lyst-mutant mice, as well as background differences between wild-type C57BL/6J and DBA/2J mice. To aid identification of potential genetic modifier genes causing these effects, we searched public datasets for cerebellar-expressed genes that are differentially expressed and/or contain potentially detrimental genetic variants. From these approaches, Nos1, Prdx2, Cbln3, Gnb1, Pttg1 were confirmed to be differentially expressed and leading candidates.

Out of Southern East Asia of the Brown Rat Revealed by Large-Scale Genome Sequencing

The geographic origin and migration of the brown rat (Rattus norvegicus) remain subjects of considerable debate. In this study, we sequenced whole genomes of 110 wild brown rats with a diverse world-wide representation. We reveal that brown rats migrated out of southern East Asia, rather than northern Asia as formerly suggested, into the Middle East and then to Europe and Africa, thousands of years ago. Comparison of genomes from different geographical populations reveals that many genes involved in the immune system experienced positive selection in the wild brown rat.

Effects of sustained daily latanoprost application on anterior chamber anatomy and physiology in mice

Latanoprost is a common glaucoma medication. Here, we study longitudinal effects of sustained latanoprost treatment on intraocular pressure (IOP) in C57BL/6J mice, as well as two potential side-effects, changes in iris pigmentation and central corneal thickness (CCT). Male C57BL/6J mice were treated daily for 16 weeks with latanoprost. Control mice were treated on the same schedule with the preservative used with latanoprost, benzalkonium chloride (BAK), or handled, without ocular treatments. IOP and CCT were studied at pre-treatment, 2 "early" time points, and 2 "late" time points; slit-lamp analysis performed at a late time point; and expression of corneal and iridial candidate genes analyzed at the end of the experiment. Latanoprost lowered IOP short, but not long-term. Sustained application of BAK consistently resulted in significant corneal thinning, whereas sustained treatment with latanoprost resulted in smaller and less consistent changes. Neither treatment affected iris pigmentation, corneal matrix metalloprotease expression or iridial pigment-related genes expression. In summary, latanoprost initially lowered IOP in C57BL/6J mice, but became less effective with sustained treatment, likely due to physiological adaptation. These results identify a new resource for studying changes in responsiveness associated with long-term treatment with latanoprost and highlight detrimental effects of commonly used preservative BAK.

Genetic modifiers as relevant biological variables of eye disorders

From early in the study of mammalian genetics, it was clear that modifiers can have a striking influence on phenotypes. Today, several modifiers have now been studied in enough detail to allow a glimpse of how they function and influence our perspective of disease. With respect to diseases of the eye, some modifiers are an important source of phenotypic variation that can elucidate how genes function in networks to collectively shape ocular anatomy and physiology, thus influencing our understanding of basic biology. Other modifiers represent an opportunity for new therapeutic targets, whose manipulation could be used to mitigate ophthalmic disease. Here, we review progress in the study of genetic modifiers of eye disorders, with examples from mice and humans that together illustrate the ubiquitous nature of genetic modifiers and why they are relevant biological variables in experimental design. Special emphasis is given to ophthalmic modifiers in mice, especially those relevant to selection of genetic background and those that might inadvertently be a source of experimental variability. These modifiers are capable of influencing interpretations of many experiments using targeted genome manipulations such as knockouts or transgenics. Whereas there are fewer examples of modifiers of eye disorders in humans with a molecular identification, there is ample evidence that they exist and should be considered as a relevant biological variable in human genetic studies as well.

A novel iris transillumination grading scale allowing flexible assessment with quantitative image analysis and visual matching

PURPOSE

To develop a sensitive scale of iris transillumination suitable for clinical and research use, with the capability of either quantitative analysis or visual matching of images.

METHODS

Iris transillumination photographic images were used from 70 study subjects with ocular or oculocutaneous albinism. Subjects represented a broad range of ocular pigmentation. A subset of images was subjected to image analysis and ranking by both expert and nonexpert reviewers. Quantitative ordering of images was compared with ordering by visual inspection. Images were binned to establish an 8-point scale. Ranking consistency was evaluated using the Kendall rank correlation coefficient (Kendall's tau). Visual ranking results were assessed using Kendall's coefficient of concordance (Kendall's W) analysis.

RESULTS

There was a high degree of correlation among the image analysis, expert-based and non-expert-based image rankings. Pairwise comparisons of the quantitative ranking with each reviewer generated an average Kendall's tau of 0.83 ± 0.04 (SD). Inter-rater correlation was also high with Kendall's W of 0.96, 0.95, and 0.95 for nonexpert, expert, and all reviewers, respectively.

CONCLUSIONS

The current standard for assessing iris transillumination is expert assessment of clinical exam findings. We adapted an image-analysis technique to generate quantitative transillumination values. Quantitative ranking was shown to be highly similar to a ranking produced by both expert and nonexpert reviewers. This finding suggests that the image characteristics used to quantify iris transillumination do not require expert interpretation. Inter-rater rankings were also highly similar, suggesting that varied methods of transillumination ranking are robust in terms of producing reproducible results.

Autophagy and Mitochondrial Dysfunction in Tenon Fibroblasts from Exfoliation Glaucoma Patients

Purpose

To test the hypothesis that autophagy dysfunction is involved in exfoliation syndrome (XFS), a systemic disorder of extracellular elastic matrices that causes a distinct form of human glaucoma.

Methods

Fibroblasts derived from tenon tissue discards (TFs) from filtration surgery to relieve intraocular pressure in XFS patients were compared against age-matched TFs derived from surgery in primary open-angle glaucoma (POAG) patients or from strabismus surgery. Differential interference contrast light, and electron microscopy were used to examine structural cell features. Immunocytochemistry was used to visualize LOXL1 and Fibulin-5, lysosomes, endosomes, Golgi, and microtubules. Light scatter, Cyto-ID^TM and JC1 flow cytometry were used to measure relative cell size, autophagic flux rate and mitochondrial membrane potential (MMPT), respectively. Enhanced autophagy was induced by serum withdrawal.

Results

In culture, XFS-TFs were 1.38-fold larger (by light scatter ratio, p = 0.05), proliferated 42% slower (p = 0.026), and were morphologically distinct in 2D and 3D culture compared to their POAG counterparts. In extended 3D cultures, XFS-TFs accumulated 8–10 times more Fibulin-5 than the POAG-TFs, and upon serum withdrawal, there were marked deficiencies in relocation of endosomes and lysosomes to the perinuclear area. Correspondingly, the XFS-TFs displayed significant accumulation of the autophagasome marker LC3 II (3.9 fold increase compared to POAG levels, p = 0.0001) and autophagic flux rate as measured by Cyto-ID dye was 53% lower in XFS-TFs than in POAG-TFs (p = 0.01), indicating reduced clearance of autophagasomes. Finally the percent of cells with diminished MMPT was 3–8 times larger in the XFS-TFs than in POAG-TFs (p = 0.02).

Conclusions

Our results provide for the first time a link between XFS pathology to autophagy dysfunction, a major contributor to multiple age related diseases systemically throughout the body, in the brain and in the retina. A diminished capacity for degradation of denatured protein and aging cellular organelles may underpin the development of extracellular protein aggregates in XFS.

Lysosomal Trafficking Regulator (LYST)

Regulation of vesicle trafficking to lysosomes and lysosome-related organelles (LROs) as well as regulation of the size of these organelles are critical to maintain their functions. Disruption of the lysosomal trafficking regulator (LYST) results in Chediak-Higashi syndrome (CHS), a rare autosomal recessive disorder characterized by oculocutaneous albinism, prolonged bleeding, severe immunodeficiency, recurrent bacterial infection, neurologic dysfunction and hemophagocytic lympohistiocytosis (HLH). The classic diagnostic feature of the syndrome is enlarged LROs in all cell types, including lysosomes, melanosomes, cytolytic granules and platelet dense bodies. The most striking CHS ocular pathology observed is an enlargement of melanosomes in the retinal pigment epithelium (RPE), which leads to aberrant distribution of eye pigmentation, and results in photophobia and decreased visual acuity. Understanding the molecular function of LYST and identification of its interacting partners may provide therapeutic targets for CHS and other diseases associated with the regulation of LRO size and/or vesicle trafficking, such as asthma, urticaria and Leishmania amazonensis infections.

Animal models of exfoliation syndrome, now and future

At present, no animal models fully embody exfoliation syndrome or exfoliation glaucoma. Both genetic and environmental factors appear critical for disease manifestation, and both must be considered when generating animal models. Because mice provide a powerful mammalian platform for modeling complex disease, this paper focuses on mouse models of exfoliation syndrome and exfoliation glaucoma.

Population genomics reveal recent speciation and rapid evolutionary adaptation in polar bears

Polar bears are uniquely adapted to life in the High Arctic and have undergone drastic physiological changes in response to Arctic climates and a hyper-lipid diet of primarily marine mammal prey. We analyzed 89 complete genomes of polar bear and brown bear using population genomic modeling and show that the species diverged only 479-343 thousand years BP. We find that genes on the polar bear lineage have been under stronger positive selection than in brown bears; nine of the top 16 genes under strong positive selection are associated with cardiomyopathy and vascular disease, implying important reorganization of the cardiovascular system. One of the genes showing the strongest evidence of selection, APOB, encodes the primary lipoprotein component of low-density lipoprotein (LDL); functional mutations in APOB may explain how polar bears are able to cope with life-long elevated LDL levels that are associated with high risk of heart disease in humans.

Genetic modulation of the iris transillumination defect: a systems genetics analysis using the expanded family of BXD glaucoma strains

We investigated the contributions of Tyrp1 and Gpnmb to the iris transillumination defect (TID) in five age cohorts of BXD mice. Using systems genetics, we also evaluated the role of other known pigmentation genes (PGs). Mapping studies indicate that Tyrp1 contributes to the phenotype at all ages, yet the TID maps to Gpnmb only in the oldest cohort. Composite interval mapping reveals secondary loci viz. Oca2, Myo5a, Prkcz, and Zbtb20 that modulate the phenotype in the age groups up to 10–13 months. The contributions of Tyrp1 and Gpnmb were highly significant in all age cohorts. Moreover, in young mice, all six gene candidates had substantial interactions in our model. Our model accounted for 71–88% of the explained variance of the TID phenotype across the age bins. These results demonstrate that along with Tyrp1 and Gpnmb, Oca2, Myo5a, Prkcz, and Zbtb20 modulate the TID in an age-dependent manner.

Atypical Chédiak-Higashi syndrome with attenuated phenotype: three adult siblings homozygous for a novel LYST deletion and with neurodegenerative disease

Background

Mutations in LYST, a gene encoding a putative lysosomal trafficking protein, cause Chédiak-Higashi syndrome (CHS), an autosomal recessive disorder typically characterized by infantile-onset hemophagocytic syndrome and immunodeficiency, and oculocutaneous albinism. A small number of reports of rare, attenuated forms of CHS exist, with affected individuals exhibiting progressive neurodegenerative disease beginning in early adulthood with cognitive decline, parkinsonism, features of spinocerebellar degeneration, and peripheral neuropathy, as well as subtle pigmentary abnormalities and subclinical or absent immune dysfunction.

Methods

In a consanguineous Pakistani kindred with clinical phenotypes consistent with attenuated CHS, we performed SNP array-based homozygosity mapping and whole gene sequencing of LYST.

Results

We identified three individuals homozygous for a novel six base pair in-frame deletion in LYST (c.9827_9832ATACAA), predicting the loss of asparagine and threonine residues from the LYST transcript (p.Asn3276_Thr3277del), and segregating with the phenotype in this family.

Conclusions

We further characterize the neurologic features of the attenuated form of CHS, and discuss pathophysiologic mechanisms underlying the neurodegenerative components of CHS. Attenuated CHS is phenotypically heterogenous and should be considered when young adults develop neurodegenerative disease and have pigmentary abnormalities. We briefly discuss surveillance and management of patients with CHS-related neurodegeneration.

Understanding lentiviral vector chromatin targeting: working to reduce insertional mutagenic potential for gene therapy

Replication-deficient retroviruses have been successfully utilized as vectors, offering an efficient, stable method of therapeutic gene delivery. Many examples exist proving this mode of integrative gene transfer is both effective and safe in cultured systems and clinical trials. Along with their success, severe side effects have occurred with early retroviral vectors causing a shift in the approach to vector design before further clinical testing. Several alternative delivery methods are available but lentiviral vectors (LV) are among the most favorable as they are already well understood. LV offer safer integration site selection profiles and a lower degree of genotoxicity, compared with γ-retroviral vectors. Following their introduction, development of the self-inactivating vector configuration was a huge step to this mode of therapy but did not confer full protection against insertional mutagenesis. As a result integration, modeling must be improved to eventually avoid this possibility. The cellular factor LEDGF/p75 seems to play an essential role in the process of LV site selection and its interactions with chromatin are being quickly resolved. LEDGF/p75 is at the center of one example directed integration effort where recombinant products bias the integration event, a step toward fully directed integration into pre-determined benign loci. A more accurate picture of the details of LEDGF/p75 in the natural integration process is emerging, including new binding specificities, chromatin interaction kinetics and additional cellular factors. Together with next-generation sequencing technology and bio-informatics to analyze integration patterns, these advancements will lead to highly focused directed integration, accelerating wide-spread acceptance of LV for gene therapy.

Complex interactions of Tyrp1 in the eye

PURPOSE

To use a systems genetics approach to construct and analyze co-expression networks that are causally linked to mutations in a key pigementation gene, tyrosinase-related protein 1 (Tyrp1), that is associated both with oculocutaneous albinism type 3 (OCA3) in humans and with glaucoma in mice.

METHODS

Gene expression patterns were measured in whole eyes of a large family of BXD recombinant inbred (RI) mice derived from parental lines that encode for wildtype (C57BL/6J) and mutant (DBA/2J) Tyrp1. Protein levels of Tyrp1 were measured in whole eyes and isolated irides. Bioinformatics analyses were performed on the expression data along with our archived sequence data. Separate data sets were generated which were comprised of strains that harbor either wildtype or mutant Tyrp1 and each was mined individually to identify gene networks that covary significantly with each isoform of Tyrp1. Ontology trees and network graphs were generated to probe essential function and statistical significance of covariation. Genes with strong covariance in wildtype mice were assembled into genome-wide heatmaps for cohorts carrying either wildtype or mutant Tyrp1.

RESULTS

Single nucleotide polymorphism (SNP) analysis verified the presence of the Tyrp1b mutation in the Tyrp1 gene. Message levels were greater in BXD strains with the mutant Tyrp1. Interval mapping of these BXD mice revealed a strong expression quantitative trait locus (eQTL) on Chr 4 at the location of the gene itself. Composite mapping revealed a suggestive eQTL on Chr 9 at the location of myosin-Va (Myo5a), mutations in which are known as dilute. Enriched biologic processes associated with wildtype Tyrp1 included pigmentation, melanin biosynthetic process, and mesenchymal cell development, while associations with the mutant gene included categories of neural crest cell development, protein metabolic processes and glycoprotein metabolic processes. Genome-wide heatmaps revealed strong candidate cis-eQTLs on Chr 4 at Tyrp1 and on Chr 9 at Myo5a in all mice. In the wildtype data set, Tyrp1 was an upstream regulator of six pigmentation and two mesenchyme genes. In addition, five genes, including Tyrp1, were at least partially regulated by Myo5a. Analyses of the strains harboring the mutant gene revealed significant loss of correlation to traditional genes and gain of correlation to genes with little or no functional relationship.

CONCLUSIONS

These findings indicate that the Tyrp1(b) mutation modifies the pathways and gene networks in which Tyrp1 functions. Our results also indicate direct and indirect regulatory control of Tyrp1 and other pigmentation and mesenchymal genes by Myo5a. Lastly, we find that the mutations reduce the ability of Tyrp1 to regulate expression of other genes that participate in pigmentation metabolism.

Anterior segment dysgenesis and early-onset glaucoma in nee mice with mutation of Sh3pxd2b

PURPOSE

Mutations in SH3PXD2B cause Frank-Ter Haar syndrome, a rare condition characterized by congenital glaucoma, as well as craniofacial, skeletal, and cardiac anomalies. The nee strain of mice carries a spontaneously arising mutation in Sh3pxd2b. The purpose of this study was to test whether nee mice develop glaucoma.

METHODS

Eyes of nee mutants and strain-matched controls were comparatively analyzed at multiple ages by slit lamp examination, intraocular pressure recording, and histologic analysis. Cross sections of the optic nerve were analyzed to confirm glaucomatous progression.

RESULTS

Slit lamp examination showed that, from an early age, nee mice uniformly exhibited severe iridocorneal adhesions around the entire circumference of the eye. Presumably as a consequence of aqueous humor outflow blockage, they rapidly developed multiple indices of glaucoma. By 3 to 4 months of age, they exhibited high intraocular pressure (30.8 ± 12.5 mm Hg; mean ± SD), corneal opacity, and enlarged anterior chambers. Although histologic analyses at P17 did not reveal any indices of damage, similar analysis at 3 to 4 months of age revealed a course of progressive retinal ganglion cell loss, optic nerve head excavation, and axon loss.

CONCLUSIONS

Eyes of nee mice exhibit anterior segment dysgenesis and early-onset glaucoma. Because SH3PXD2B is predicted to be a podosome adaptor protein, these findings implicate podosomes in normal development of the iridocorneal angle and the genes influencing podosomes as candidates in glaucoma. Because of the early-onset, high-penetrance glaucoma, nee mice offer many potential advantages as a new mouse model of the disease.

Noninvasive assessment of vascular structure and function in conscious rats based on in vivo imaging of the albino iris

Experimental techniques allowing longitudinal studies of vascular disease progression or treatment effects are not readily available for most animal models. Thus, most existing studies are destined to either study individual time points or use large cohorts of animals. Here we describe a noninvasive technique for studying vascular disease that is based on in vivo imaging of the long posterior ciliary artery (LPCA) in the iris of albino rats. Using a slit-lamp biomicroscope, images of the LPCA were taken weekly in conscious normotensive Wistar Kyoto rats (WKY, n = 10) and spontaneously hypertensive rats (SHR, n = 10) for 10 wk. Using imaging software, we found that lumen diameter was significantly smaller and the wall-to-lumen (W/L) ratio larger in SHR than in WKY. Wall thickness was not different. Blood pressure correlated with the W/L ratio. Histology of the abdominal aorta also revealed a smaller lumen diameter and greater W/L ratio in SHR compared with WKY. Corneal application of the muscarinic receptor agonist pilocarpine elicited a dose-dependent vasodilation of the LPCA that could be antagonized by inhibition of nitric oxide synthase, suggesting that the pilocarpine response is mainly mediated by endothelium-derived nitric oxide. Consistent with endothelial dysfunction in SHR, pilocarpine-induced vasodilation was greater in WKY rats than in SHR. These findings indicate that in vivo imaging of the LPCA allows assessment of several structural and functional vascular parameters in conscious rats and that the LPCA responds to disease insults and pharmacologic treatments in a fashion that will make it a useful model for further studies.

Microarray analysis of iris gene expression in mice with mutations influencing pigmentation

PURPOSE

Several ocular diseases involve the iris, notably including oculocutaneous albinism, pigment dispersion syndrome, and exfoliation syndrome. To screen for candidate genes that may contribute to the pathogenesis of these diseases, genome-wide iris gene expression patterns were comparatively analyzed from mouse models of these conditions.

METHODS

Iris samples from albino mice with a Tyr mutation, pigment dispersion-prone mice with Tyrp1 and Gpnmb mutations, and mice resembling exfoliation syndrome with a Lyst mutation were compared with samples from wild-type mice. All mice were strain (C57BL/6J), age (60 days old), and sex (female) matched. Microarrays were used to compare transcriptional profiles, and differentially expressed transcripts were described by functional annotation clustering using DAVID Bioinformatics Resources. Quantitative real-time PCR was performed to validate a subset of identified changes.

RESULTS

Compared with wild-type C57BL/6J mice, each disease context exhibited a large number of statistically significant changes in gene expression, including 685 transcripts differentially expressed in albino irides, 403 in pigment dispersion-prone irides, and 460 in exfoliative-like irides.

CONCLUSIONS

Functional annotation clusterings were particularly striking among the overrepresented genes, with albino and pigment dispersion-prone irides both exhibiting overall evidence of crystallin-mediated stress responses. Exfoliative-like irides from mice with a Lyst mutation showed overall evidence of involvement of genes that influence immune system processes, lytic vacuoles, and lysosomes. These findings have several biologically relevant implications, particularly with respect to secondary forms of glaucoma, and represent a useful resource as a hypothesis-generating dataset.

Spectral analysis by XANES reveals that GPNMB influences the chemical composition of intact melanosomes

GPNMB is a unique melanosomal protein. Unlike many melanosomal proteins, GPNMB has not been associated with any forms of albinism, and it is unclear whether GPNMB has any direct influence on melanosomes. Here, melanosomes from congenic strains of C57BL/6J mice mutant for Gpnmb are compared to strain-matched controls using standard transmission electron microscopy and synchrotron-based X-ray absorption near-edge structure analysis (XANES). Whereas electron microscopy did not detect any ultrastructural changes in melanosomes lacking functional GPNMB, XANES uncovered multiple spectral phenotypes. These results directly demonstrate that GPNMB influences the chemical composition of melanosomes and more broadly illustrate the potential for using genetic approaches in combination with nano-imaging technologies to study organelle biology.